Particle sensing apparatus, method and flow direction collar therefor

ABSTRACT

A flow direction collar is positionable in an electrical zone sensing apparatus with an elongated bore therein disposed in substantial alignment with an aperture through which particles carried by a liquid pass while being electrically sensed. The collar is positioned immediately upstream of the aperture to cause a directional flow of the liquid along a path substantially parallel to a longitudinal axis for the aperture. The flow through the collar directs the particles to flow along paths substantially parallel to the aperture axis thereby reducing the turbulence about the particle created by abrupt changes in velocity. Preferably, the collar includes a housing for telescoping on the bottom of a detection tube.

i States mite 1 Karuhn et al.

[ PARTICLE SENSING APPARATUS,

METHOD AND FLOW DIRECTION COLLAR THEREFOR [75] Inventors: Richard F.Karuhn, Chicago; Reg

Davies, Justice, both of Ill.; Brian Howard Kaye, Sudbury, Ontario,

Canada [73] Assignee: IIT Research Institute, Chicago, Ill.

[22] Filed: Aug. 20, 1971 [21] Appl. No.: 173,575

[52] US. Cl. 324/71 CP [51] Int. Cl. G0ln 27/00 [58] Field of Search324/71 R, 71 CP [56] References Cited OTHER PUBLICATIONS Spielman etal.; J. Colloid & Interface Sci.; v. 26, pp. 175-182(1968) Primary Exarr zjperAlfred E. Smith Attorney-William B. Anderson, Edwin M. Luedekaand James J. Hamill et al.

[57] ABSTRACT A flow direction collar is positionable in an electricalzone sensing apparatus with an elongated bore therein disposed insubstantial alignment with an aperture through which particles carriedby a liquid pass while being electrically sensed. The collar ispositioned immediately upstream of the aperture to cause a directionalflow of the liquid along a path substantially parallel to a longitudinalaxis for the aperture. The flow through the collar directs the particlesto flow along paths substantially parallel to the aperture axis therebyreducing the turbulence about the particle created by abrupt changes invelocity. Preferably, the collar includes a housing for telescoping onthe bottom of a detection tube.

11 Claims, 10 Drawing Figures 8523? DETECTOR COUNTER l\ 1 I 75 2o 73PATENTEDJUN12 I973 SiEEI 2 N 2 FIG 5A PARTICLE SIZE PARTICLE SIZE FIG.4A

FIG.4

ATTYS.

1 PARTICLE SENSING APPARATUS, THO!) AND lFLQW DIRECTION COLLAR THEREFORThis invention relates to detecting and sizing microscopic particles ina liquid medium with an electrical zone sensing apparatus and moreparticularly to a manner of controlling the flow of particles in fluidthrough a particle sensing zone of such an apparatus.

In copending application of Karuhn et al. filed of even date, entitledMethod Of And Apparatus For Detecting And Sizing Microscopic Particles,and assigned to the assignee of this application, improved accuracy insensing and sizing of microscopic particles was attained over thatpreviously attained with a known kind of electrical zone sensing counterof the general type shown and described in US. Pat. No. 2,656,508. Morespecifically, it was found that particles flowing at an angle to theaxis of the sensing zone aperture and about a sharp edge on the inletside of the aperture were producing turbulence, also turbulent fluidflow was occurring, and that the particles were being detected as anelectrical pulse which was the combined result of both,

the particles present and the turbulence. In some instances, the tinyvoltages due to the turbulence actually gave the appearance of tinyparticles within the electrolyte fluid.

As disclosed in the aforesaid copending application, improved accuracyof size measurement and size distribution may be obtained by providingflow control director means upstream of the aperture to provide a morestreamline, less turbulent flow of electrolyte through the aperture andto guide the particles to flow along a path substantially parallel tothe axis of the aperture. The flow control means illustrated in theaforesaid application is in the form of a smooth tapered flow directorinlet wall blended with the aperture to remove the sharp edge effect atthe prior art aperture and to provide laminar fluid flow propertiesthrough the aperture; and this also resulted in the electrical sensingmeans producing a regularly occurring pulse of more ideal shape. Theflow director inlet wall in the aforesaid application was formed in asapphire wafer in which the aperture was also formed and the two weresmoothly blended at a transition zone therebetween. The aperture wasgenerally cylindrical in shape.

To substitute the new wafer disclosed in the aforesaid application forthe conventional wafer already in existing equipment, is not always easyas these wafers are often fused to a glass receiving tube. Thus, it maybe difficult for some persons to modify their existing equipment toachieve the improved resolution. Therefore, a need exists for aninexpensive flow straightener means which can be readily used withexisting counters of the kind described.

Accordingly, a general object of the present invention is to provide asimple and inexpensive device for improving the accuracy of anelectrical zone sensing apparatus.

These and other objects of the invention will become apparent withreference to the following detailed description and accompanyingdrawings, in which:

FIG. 1 is a schematic representation of an apparatus for detecting andsizing microscopic particles;

FIG. 2 is an enlarged, sectional, elevational view of a portion of theapparatus shown in FIG. 1;

FIG. 3 is a diagrammatic view of the scanner portion of a prior artdevice;

FIG. 4 is a graphical representation of an abnormal pulse shape for asingle particle detected with the prior art device of FIG. 3;

FIG. 4A is a more ideal pulse shape detected for a single particle whenusing the apparatus of FIG. 1;

FIG. 5 is a graphical representation of particle frequency distributionobtained with a prior art device;

FIG. 5A is a graphical representation of particle frequency distributionobtained with the present invention;

FIG. 6 is a graphical representation of particle frequency distributionobtained with the apparatus shown in FIG. 1 with the particles enteringat varying angles to the orifice axis;

FIG. 7 is a fragmentary, enlarged, sectional view of another apparatusfor detecting and sizing microscopic particles; and

FIG. 8 is a graphical representation of the effect of particles detectedusing the apparatus shown in part in FIG. 7.

As shown in the drawings for purposes of illustration, the invention isembodied in an apparatus 10 for detecting and measuring the size and thefrequency of distribution of microscopic particles suspended in a fluidmedium such as a liquid electrolyte. Very generally, the illustratedapparatus 10 comprises a vessel 12 such as a beaker containing theelectrolyte and the suspended particles which are to be analyzed. Theelectrolyte containing the particles in the vessel is drawn through asmall aperture 15 in a scanner element 14 into a receiver tube 17. Theliquid flow through the scanner element 14 is caused by a fluid head,i.e. a pressure differential, such as by applying reduced pressure froma vacuum line 18 to the upper surface of the liquid in the tube. Tomeasure the change in conductivity caused by a particle passing throughthe aperture 15 in the scanner element, there is provided an electricalcircuit means including a detector circuit 20 which is connected to anelectrode 22 projecting into the electro lyte in a vessel and anelectrode 24 projecting into the electrolyte in the tube.

In accordance with the present invention, improved accuracy in sizemeasurement and size distribution has been obtained by addition of asimple and inexpensive flow straightener means in the form of a flowdirection collar 25 to a conventional electrical zone sensing apparatus.More specifically, the flow direction collar is positioned with anelongated bore 27 therein disposed in substantial alignment with theaxis of the aperture 15 to cause a directional flow thereby reducingparticle induced turbulence in the electrolyte flowing from the vessel12 into the detection tube 17 that is obtained without the flowdirection collar 25. The flow direction collar also serves to direct theparticles to flow along paths substantially parallel to an axis 31through the circular aperture 15 in the scanner element 14. Tofacilitate positioning of the flow directing bore 27 in alignment withthe aperture 15, the illustrated flow directing collar has a housing 33with a cylindrical chamber 34 for telescoping on the bottom of thedetection tube 17. In this instance, the flow directing bore 27comprises a large outer diameter section 33 and an inner restricteddiameter section 35.

Also, in accordance with this invention, improved results may beobtained by providing a micro-mesh screen 39 for filtering particles ordebris from the liquid flowing through the bore 27 which would be toolarge to pass readily through the aperture 15. By filtering the largeparticles and debris from the'electrolyte, turbulence which results if aparticle is lodged at the entrance to the aperture 15 is avoided.

Referring now in greater detail to the flow direction collar 25, itshousing 33 is generally cylindrical with a cylindrical wall 43telescoped about a lower end 45 of the detection tube 17 with a bottomwall 47 of the tube abutting inner side 49 of a bottom wall 51 for thehousing 33. Preferably, the housing 33 is formed of a plastic such ashigh density polyethylene and is molded with the cylindrically shapedchamber 34 defined within the cylindrical wall 43.

To prevent the flow of electrolyte an particles into cylindrical chamber34 through a top opening 53 in the housing 33, a sealing means 55 isprovided. The illustrated sealing means is in the form of a pair ofrings 57 which are seated in annular grooves in the cylindrical wall 43adjacent the top of the housing. Thus, the flow of electrolyte from thevessel into the interior chamber of the housing 33 must be by way ofpassage through the screen 39 and the flow directing bore 27.

Referring now in greater detail to the micro-mesh screen 39, it ispositioned at the entrance to the outer large diameter section 35 of theilow directing bore 27 in an enlarged annular seat 59 into which is alsopositioned an O ring 61 to tightly secure the screen within the seat toprevent particles passing around the screen. Preferably, the screen issubstantially larger in diameter than the diameter of the restrictedsection 35 to assure that no turbulence in the fluid flow is due to thescreen.

The illustrated screen 39 is a micro-mesh screen having openings lessthan or equal to orifice size in larger dimension so that most of theparticles being sized can readily pass through the screen with theelectrolyte. The function of the screen is to prevent the movement oflarge particles to the aperture as would lodge at the entrance to theaperture and create turbulent flow.

Referring now in greater detail to the illustrated apparatus, the vessel12 comprises a beaker or other receptacle of insulating material, suchas glass, which is adapted to contain an electrically conductive liquidin which the particles to be detected and measured are scattered andsuspended. In the examples given herein, the electrically conductiveliquid or electrolyte is sodium chloride in which are latex particles ofabout 2.68 microns in diameter are suspended, although other suitableelectrolytes can be used. The particles are scattered in the electrolyteso that groups of particles do not influence electrical sensing by thedetector 2th. The liquid and the particles are of different conductivityusually in magnitude of several different orders so that current orvoltage change can be measured by the detector as a function of changein conductivity. The detection tube 117 for receiving the fluid is alsoof insulating material, such as glass, and the tube rests within thevessel. In this instance, a lower side wall of the tube 17 is flattenedto provide a flat wall till, as best seen in FIG. 2', at its lower endand a stopper 63 (FIG. 1) closes the upper end of the tube. In theflattened wall 61, an opening 65 is formed and spaced from the bottom ofthe tube. Preferably, the seal rings 57 engage the detection tube 17 ata circular cross section immediately above the flattened wall fill andprevent liquid flow therepast into the chamber 34).

The scanner element 114 is mounted such as by a suitable adhesive orfusion technique to the flat wall 61 with its aperture 35 in registerwith a central portion of the larger diameter opening 65 in thedetecting tube 17. A rear side 67 of the scanner element covers theopening except at an outlet end 69 of the aperture 15. Thus, a path offluid flow is defined from the vessel 12, through flow direction collar25, aperture 15 and the tube wall opening 65 into the detection tube 17.As a difference in fluid head is established between the vessel and thetube, preferably by drawing through the pipe 18 a vacuum on the surfaceof the liquid in the tube, the liquid and particles are induced to flowbetween the vessel and tube.

In the illustrated embodiment, the scanner element 14 comprises a smallblock or wafer 71 of sapphire or another inert element. The wafer may befused to the flattened wall 61 of the tube wall, the tube preferablybeing fabricated of a heat-resistant glass to receive the fused sapphirewafer without damage. The cylindrical aperture 15 may be formed bydrilling or by other known methods. The aperture 15 is typically betweenabout 30 to 560 microns in diameter, and the length of the aperture isabout equal to the dimension of the aperture diameter.

The detector 20 electrically senses, measures, and amplifies signalsproduced by changes in resistance in the aperture 15 due to particlespassing therethrough. It is operatively connected to the electrode 22disposed in the vessel 12 and to the electrode 24 located in the tube17, both electrodes being immersed in the electrolyte. The detector 20is further operatively connected to a counter 73 which totals the numberof signals. A current source 75 operates the detector 20 and the counter73. A cathode ray oscilloscope (not shown) can be utilized to visuallydisplay the shape of the current or voltage pulses which have beendetected. Circuitry for the detection and measurement of particlesignals is well known and any suitable system can be employed.

As each particle passes through the aperture 15, it displaces its ownvolume of the electrically conductive liquid within the aperture. As theliquid and particles are of different conductivity and resistance, anddisplacement of one by the other results in a momentary change in thedetected resistance between the electrodes 22 and 24 on either side ofthe aperture. This resistance change produces a voltage pulse of shortduration having a magnitude proportional to particle volume, if thecurrent is kept constant. It should be noted that the method may alsocomprise maintaining the voltage constant while detecting a change inmeasured current. Accordingly, voltage pulse height is proportional toamplifier gain, aperture current and the resistance change indicatedupon passage of a particle through the aperture.

Thus,

AE= GI AR,

where AE voltage pulse height G amplifier gain I aperture current ARchange in resistance, and

AR poVlA [l/(1-po/p) a/Al where p0 electrolyte resistivity V particlevolume (the particle being a right cylinder having its axis aligned withand shorter than the aperture axis) A area of the aperture normal to itsaxis p effective particle resistivity a area of the particle takennormal to the aperture axis as oriented in the aperture.

It can be seen that, theoretically, response to passage of a particlethrough the aperture is substantially linear with particle size,provided that the particle has less than about 40 percent of thediameter of the aperture. To ensure that the change in current orvoltage induced by the passage of the particles through the aperture isdependent substantially on particle size, the fluid medium is chosen sothat particle resistivity is effectively several orders of magnitudegreater than liquid resistivity.

It has been found that electrical charge, surface films, porosity of theparticles and temperature of the liquid have little effect on responseor can be readily compensated for. Also, the particle shape and internalstructure do not greatly affect size measurement.

Disturbances frequently occur which result in a voltage change largerthan expected for a particle of a given size. These disturbancesincrease the standard deviation of the particle size distribution, whencompared with that determined by an electron microscope. Generally, suchdisturbances are observed when particles do not pass through thecylindrical aperture 15 parallel to its axis and accordingly createareas of turbulence about the particles. If the particles enter thescanner element 14 at an angle to the aperture axis 31, interactionoccurs between a sharp edge 79, as best seen in FIG. 3, of the scannerelement in which the aperture is formed, the particle, and the liquid,which interaction produces turbulence about the particle usually becauseof an abrupt increase in the velocity of the particle. Also, a vortexarea 81 is created just inside the entrance to the cylindrical apertureby the electrolyte liquid flowing past the sharp edge and separatinginto streams and a turbulence results in this region producing thedisturbances or noise or false signals. Such liquid turbulence can bereduced by eliminating the sharp edge and providing a smooth contouredsurface at the aperture inlet as described in the aforesaid copendingapplication. When the pulse produced by the particle induced turbulenceis added to the voltage pulse produced by the particle, a pulse muchlarger and of a different shape than the theoretical pulse shaperesults. The turbulence pulses might also be counted as additional smallparticles. On the other hand, particles entering the aperture 15parallel to the axis thereof produce a pulse height and shape similar tothe theoretical height and shape. Accordingly, elimination of thisturbulence pulse permits more accurate reading and lowering thethreshold of size detection.

A commercially available electrical zone sensing apparatus generallysimilar to that disclosed in FIG. I but without the flow directingcollar 25 and having the scanner element 14 shown in FIG. 3 will bedescribed as to the pulse shapes and frequency distribution curvesobtained therewith. As best seen in FIG. 3, the fluid medium passes inthe direction shown by the arrow through the aperture 15 in the scannerelement 14, the entrance to which is defined by the sharp edge 79. Theturbulence caused by the particle and electrolyte flow past the sharpedge is indicated in the pulse 83 (FIG.

4), which is a graph of detected current versus position of the particlewithin the aperture. More particularly, the pulse 33 includes a smallpeak 84 which adds to the overall height of the pulse making it ofgreater height than a similar but more ideal pulse shape 85 obtainedwhen using the flow straightening means of the present invention.

Many of the particles passing through the aperture i5 of the scannerelement 14 of the prior art device along paths parallel to the apertureaxis produce a normal pulse but it is the frequency of the abnormalpulse shapes due to the turbulence which results in a lack of accuracyin measurement which will be described in connection with the graphsshown in FIGS. 5 and 8. The peaked particle distribution curve shown inFIG. 5 obtained with the scanner element 14 of FIG. 3 without the flowstraightening means is wider at its base and is wider at the top of thepeak 86 than is the peaked curve 88 shown in FIG. 5A obtained with theflow directing collar 25. The curve of FIG. 5A is a more accuraterepresentation of particle size frequency than is the curve of FIG. 5 asthe particles detected have been previously sized by other apparatus.Providing the flow direction collar 25 thus results in substantiallyaxial flow of the fluid and particle thereby reducing turbulence aboutthe particles which results from an abrupt change in velocity when itsdirection is changed to axial, and accordingly negation of noise, evenif a particle initially enters the collar along a line other thansubstantially parallel to the aperture axis 31.

If the flow direction collar is properly positioned such that its bore27 and the aperture I5 are in register, substantially non-turbulentparticle flow will occur and good resolution of size distribution willbe achieved, as illustrated by the solid line curve 9] in FIG. 6. On theother hand, if the collar is improperly positioned or deliberatelymispositioned and the particles are directed into the aperture 17 at anangle of about 5 to the aperture axis, the mean particle size willappear to increase and good resolution of size distribution will not beattained. Dotted line curve 93 in FIG. 6 illustrates the resultsachieved when the flow direction collar 25 was turned 5 from a positionin which its flowing directing bore 27 was substantially aligned withthe axis 31 of the aperture 15 and hence in this position the particlesflowing through the bore 27 are deliberately guided along a path at a 5angle to the aperture axis 31. The mean particle increase is due tonoise created by the particles not following a path aligned with theaperture axis. By turning the collar 25 to a position in which its boreaxis was 50 from the axis 31, particles were directed along a path at anangle of about 50 to the aperture axis; and the mean particle sizeincreased to an even greater extent and the size distribution wasgrossly inaccurate as indicated by the dotted line curve 95 shown inFIG. 6. Thus, the value of flow straightening in achieving greateraccuracy in size measurement and the achieving of an extension ofparticle size range was demonstrated.

A further embodiment of the invention is illustrated in FIG. '7. In thisembodiment, the scanner element 114 of the conventional kind has beenreplaced with a scanner element Ma of the kind disclosed in theaforesaid copending application to reduce the electrolyte turbulencecaused by the liquid flowing about the sharp edge of the aperture. Thescanner element Ma has a short cylindrical aperture 15a defined by acylindrical wall 9'7 and a contoured, smoothly-curved, inlet wall 99converging from a large diameter inlet opening 100 to a smooth blendedintersection 101 with the aperture defining wall 97. This eliminates thesharp, leading edge effect of the entrance edge 79, FIG. 3, and causes amore uniform particle approach to the aperture a thereby eliminatingedge effects which results in turbulence and noise. The combination ofthe flow direction collar 25 and flow directing wall 99 has been foundto substantially reduce both fluid turbulence and particle turbulence,more specifically, fluid flowing through the bore 27 in the collar 25 isstraightened to flow parallel to the axis 35 of the aperture prior toits passage into the curved smooth wall 99 and the particles do notexperience turbulence by flowing past the sharp edge of the apertures ofthe prior art.

The contoured wall 99 preferably has a maximum diameter at its inletopening 100 equal to about five times the aperture diameter and thecontoured wall flares inwardly and smoothly into the aperture. Thecontoured wall preferably has a length about twice the length of theaperture and its axis is aligned with the axis of the bore 27 and theaperture axis 35. The length of the flow directing bore 27 is preferablyat least about one onehalf times the diameter of the bore and the bore27 is preferably substantially larger in diameter than the diameter ofthe aperture 15a.

When the electrical zone sensing apparatus is provided with both theflow straightening collar 25 and the contoured orifice wall 99, the bestresults are obtained from the standpoints of more uniform and idealparticle wave shapes, such as the wave shape shown in FIG. 4a and offiner resolution of particle distribution curves such as illustrated inFIG. 8 by the curve 103. The better resolution of particle size versusfrequency of occurrence can be best understood in connection with acomparison of the curves shown in FIGS. 5, 5a and 8. It will be recalledthat the curve 86 shown in FIG. 5 was obtained without the flowdirection collar 25 and without the contoured orifice while curve 104shown in FIG. 5a was obtained when using the flow direction collar 25without the contoured orifice. The curve 103 shown in FIG. 8 not onlyhas a narrow base like that of the curve 104 of FIG. 5a as a result ofusing the flow direction collar 25 but also includes a secondary peak107. This secondary peak was known to be statistically valid for thesample being tested and it was verified by testing the samples in othermanners. The secondary peak 105 was not in evidence, however when usinga prior art aperture shown in FIG. 3 with the conventional electricalzone sensing apparatus. Thus, the improved accuracy of resolutionillustrated by the curve 103 shown in FIG. 8 is thought to be theproduct of elimination of both particle turbulence caused by the sharpedge effect at the inlet side of the aperture and fluid turbulencecaused by non-laminar non-directed fluid flow into the aperture.

The term flow straightening means has been used herein as a generic termto refer to devices such as the illustrated simple flow directing collardevice which is secured to the detection tube 17 to provide the flowdirectional characteristics desired. The flow direction collar may, ofcourse, be positioned in other manners than be telescoping on the bottomof the detection tube to align the axis of its bore with the axis of theaperture. Also, it is within the purview of the invention that the flowstraightening means be formed in devices which would not normally beconsidered or termed a collar but which have a flow control bore ormeans.

From the foregoing, it will be seen that the present invention providesan improved method and apparatus for detecting and sizing microscopicparticles. The flow directing collar may be readily installed onexisting electrical zone sensing apparatus to reduce turbulence and todirect the particles to flow along a path substantially aligned with theaxis of the aperture in the scanner element of the apparatus. Thisresults in greater accuracy and an extension of the particle size rangewhich can be measured.

While several embodiments of the invention have been shown anddescribed, it should be apparent that various modifications could bemade therein without departing from the scope of the invention.

Various of the features of the invention are set forth in the followingclaims.

What is claimed is:

1. In an apparatus for electrically sensing and sizing microscopicparticles suspended in a fluid medium, the combination comprising meansfor containing the fluid medium and suspended particles to be sensed andsized, receiving means for receiving the fluid medium and particlessubsequent to the sensing and sizing thereof, means defining an apertureinterconnecting in fluid communication said containing means and saidreceiving means and through which said particles pass to be sensed andsized in the course of travel from said containing means to saidreceiving means, a flow straightening means associated with saidreceiving means and positioned at an inlet end for said aperture andhaving a bore substantially aligned with the axis of said aperture fordirecting the fluid medium and particles to flow in a directionsubstantially parallel to said axis means for electrically sensing theflow directed particles passing through said aperture and for takingsize measurements of the particles, and means for securing said flowstraightening means with said receiving means to cause all of the fluidmedium to travel through said bore in said fluid straightening meansbefore traveling-through said aperture.

2. An apparatus in accordance with claim 1 further comprising a screenmounted in said bore for filtering particles which are too large to passthrough said aperture.

3. An apparatus in accordance with claim 1 in which said bore of saidflow straightening means is relatively elongated and has a diameter ofat least about one onehalf times the diameter of said aperture.

4. An apparatus in accordance with claim 1 in which said flowstraightening means comprises a flow direction collar having a housingwith a hollow chamber therein with an open top and in which saidreceiving means comprises a detection tube telescoped through said opentop into said hollow chamber of said housing.

5. An apparatus in accordance with claim 1 in which said receiving meanscomprises a generally cylindrical tube, said flow straightening means isan attachment secured to said receiving means.

6. In an apparatus for electrically sensing and sizing microscopicparticles suspended in a fluid medium, the combination comprising meansfor containing the fluid medium and suspended particles to be sensed andsized, receiving means for receiving the fluid medium and particlessubsequent to the sensing and sizing thereof, means defining an apertureinterconnecting in fluid communication said containing means and saidreceiving means and through which said particles pass to be sensed andsized in the course of travel from said containing means to saidreceiving means, a flow straightening means associated with saidreceiving means and positioned at an inlet end for said aperture andhaving a bore substantially aligned with the axis of said aperture fordirecting the fluid medium and particles to flow in a directionsubstantially parallel to said axis, means for electrically sensing theflow directed particles passing through said aperture and for takingsize measurements of the particles, said flow straightening meanscomprising a flow direction collar having a housing with a hollowchamber therein with an open top, said receiving means comprising adetection tube telescoped through said open top into said hollow chamberof said housing, said flow directing bore comprising an innercylindrical section formed in said housing of a diameter smaller thanthe diameter for a large outer cylindrical section formed in saidhousing.

7. An apparatus in accordance with claim 6 in which a filter is disposedat said outer section to filter large particles and debris from thefluid medium flowing through said inner cylindrical section.

8. A flow direction collar for attachment to a detection tube of anelectrical zone sensing apparatus having an aperture through which fluidand particles may pass to be sized or counted, said collar comprising,means for securing said collar to said detection tube, and meansdefining an elongated flow-directing bore on said collar for substantialalignment with a central axis for said aperture to cause fluid to bedirected to flow in a direction parallel to said axis and to cause saidparticles to flow along paths substantially aligned with the axis ofsaid aperture.

9. A flow direction collar for attachment to a detection tube of anelectrical zone sensing apparatus having an aperture through which fluidan particles may pass to be sized or counted, said collar comprising,means for securing said collar to said detection tube, and meansdefining an elongated flow-directing bore on said collar for substantialalignment with a central axis for said aperture to cause fluid to bedirected to flow in a direction parallel to said axis and to cause saidparticles to flow along paths substantially aligned with the axis ofsaid aperture, said means for attachment to said detection tubecomprising a housing having a opening therein to telescopingly receive alower end of said detection tube, said flow directing bore also beingformed in a side wall of said housing.

10. A method for electrical sensing and determining the size of smallparticles suspended in liquid within a large vessel by passage through aflow straightening means and through an aperture having a longitudinalaxis into a receiving means, said method comprising the steps of:

suspending the particles throughout the liquid carrying the particlesthrough said aperture, inducing the liquid upstream of said aperture topass through an elongated bore in a flow directing means, directingparticles flowing with the fluid in said elongated bore to flow alongstreamline paths substantially parallel with the axis of said aperture,

inducing fluid leaving said elongated bore to flow through the apertureand to carry the suspended particles through said aperture along pathssubstantially parallel to the axis of the aperture and into saidreceiving means, and

electrically sensing and measuring the size characteristics of theparticles passing through said aperture.

11. A method in accordance with claim 10 including a further step offiltering debris and particles from said liquid prior to movementthrough said flow directing collar.

UNITED STATES PATENT oEETcE EEETTETEATE 0F cEQTm Patent No. 3 ,739 268Dated qune l2 1973 Inventor) Richard F. Karuhn, Reg Davies and Brian H.Kaye It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 3, line 14, "an" should be -and-.

Column 7, line 64, "be" should be by.

Claim 1, column 8, line 36, a comma should be inserted after "axis",

Signed and sealed this 27th day of November 1973.

(SEAL) Attest EDWARD M.PLETHER,JR. RENE D. 'I'EGTMIEYIER AttestingOfficer Acting Commissioner of Patents FORM PC4050 (w'sg) USCOMM-DC60376-P69 U.S. GOVE RNL 4ENT PRINTING OFFICE: [969 0-366-334,

1. In an apparatus for electrically sensing and sizing microscopic particles suspended in a fluid medium, the combination comprising means for containing the fluid medium and suspended particles to be sensed and sized, receiving means for receiving the fluid medium and particles subsequent to the sensing and sizing thereof, means defining an aperture interconnecting in fluid communication said containing means and said receiving means and through which said particles pass to be sensed and sized in the course of travel from said containing means to said receiving means, a flow straightening means associated with said receiving means and positioned at an inlet end for said aperture and having a bore substantially aligned with the axis of said aperture for directing the fluid medium and particles to flow in a direction substantially parallel to said axis means for electrically sensing the flow directed particles passing through said aperture and for taking size measurements of the particles, and means for securing said flow straightening means with said receiving means to cause all of the fluid medium to travel through said bore in said fluid straightening means before traveling through said aperture.
 2. An apparatus in accordance with claim 1 further comprising a screen mounted in said bore for filtering particles which are too large to pass through said aperture.
 3. An apparatus in accordance with claim 1 in which said bore of said flow straightening means is relatively elongated and has a diameter of at least about one one-half times the diameter of said aperture.
 4. An apparatus in accordance with claim 1 in which said flow straightening means comprises a flow direction collar having a housing with a hollow chamber therein with an open top and in which said receiving means comprises a detection tube telescoped through said open top into said hollow chamber of said housing.
 5. An apparatus in accordance with claim 1 in which said receiving means comprises a generally cylindrical tube, said flow straightening means is an attachment secured to said receiving means.
 6. In an apparatus for electrically sensing and sizing microscopic particles suspended in a fluid medium, the combination comprising means for containing the fluid medium and suspended particles to be sensed and sized, receiving means for receiving the fluid medium and particles subsequent to the sensing and sizing thereof, means defining an aperture interconnecting in fluid communication said containing means and said receiving means and through which said particles pass to be sensed and sized in the course of travel from said containing means to said receiving means, a flow straightening means associated with said receiving means and positioned at an inlet end for said aperture and having a bore substantially aligned with the axis of said aperture for directing the fluid medium and particles to flow in a direction substantially parallel to said axis, means for electrically sensing the flow directed particles passing through said aperture and for taking size measurements of the particles, said flow straightening means comprising a flow direction collar having a housing with a hollow chamber therein with an open top, said receiving means comprising a detection tube telescoped through said open top into said hollow chamber of said housing, said flow directing bore comprising an inner cylindrical section formed in said housing of a diameter smaller than the diameter for a large outer cylindrical section formed in said housing.
 7. An apparatus in accordance with claim 6 in which a filter is disposed at said outer section to filter large particles and debris from the fluid medium flowing through said inner cylindrical section.
 8. A flow direction collar for attachment to a detection tube of an electrical zone sensing apparatus having an aperture through which fluid and particles may pass to be sized or counted, said collar comprising, means for securing said collar to said detection tube, and means defining an elongated flow-directing bore on said collar for substantial alignment with a central axis for said aperture to cause fluid to be directed to flow in a direction parallel to said axis and to cause said particles to flow along paths substantially aligned with the axis of said aperture.
 9. A flow direction collar for attachment to a detection tube of an electrical zone sensing apparatus having an aperture through which fluid an particles may pass to be sized or counted, said collar comprising, means for securing said collar to said detection tube, and means defining an elongated flow-directing bore on said collar for substantial alignment with a central axis for said aperture to cause fluid to be directed to flow in a direction parallel to said axis and to cause said particles to flow along paths substantially aligned with the axis of said aperture, said means for attachment to said detection tube comprising a housing having a opening therein to telescopingly receive a lower end of said detection tube, said flow directing bore also being formed in a side wall of said housing.
 10. A method for electrical sensing and determining the size of small particles suspended in liquid within a large vessel by passage through a flow straightening means and through an aperture having a longitudinal axis into a rEceiving means, said method comprising the steps of: suspending the particles throughout the liquid carrying the particles through said aperture, inducing the liquid upstream of said aperture to pass through an elongated bore in a flow directing means, directing particles flowing with the fluid in said elongated bore to flow along streamline paths substantially parallel with the axis of said aperture, inducing fluid leaving said elongated bore to flow through the aperture and to carry the suspended particles through said aperture along paths substantially parallel to the axis of the aperture and into said receiving means, and electrically sensing and measuring the size characteristics of the particles passing through said aperture.
 11. A method in accordance with claim 10 including a further step of filtering debris and particles from said liquid prior to movement through said flow directing collar. 